This invention relates to an occupant protective system for automotive vehicles, and more particularly to an occupant protective system of the kind which protects occupants by inflating an air bag when the automotive vehicle is involved in a crash.
Conventionally, there has already been proposed an air bag system for automotive vehicles, as shown in FIG. 1. The air bag system comprises a control unit 100 including an acceleration sensor 101 for sensing a shock resulting from a crash of the vehicle, and a gas generator 103 including a squib 102 which is energized upon a crash of the vehicle for igniting the gas generator 103 to cause the same to generate a gas for inflating an air bag, not shown. The acceleration sensor 101 of the control unit 100 and the squib 102 of the gas generator 103 are electrically connected together via two signal lines 105 and 106. The gas generator 103 is mounted together with the air bag on a steering wheel, not shown, which rotates. According to this air bag system, in order to electrically connect portions of the signal lines 105 and 106 on the side of the squib 102 of the gas generator 103 mounted on the steering wheel, to portions of the signal lines 105 and 106 on the side of the control unit 100, which does not rotate, a cable reel 107 in which a harness of portions of the signal lines 105 and 106 is coiled is mounted on the steering wheel.
However, since the two signal lines 105 and 106 are arranged such that they extend substantially parallel and close to each other within the harness, a short circuit can be formed, though very rarely, between a point of the signal line 105 within the harness and a point of the signal line 106 within the harness or between other points of these signal lines due to manufacturing errors etc., which renders the air bag system inoperative. In the meanwhile, in the above prior art, the resistance R.sub.2 of the squib 102, which is connected in series with a monitoring resistance R.sub.1 of the acceleration sensor 101, is much smaller than the resistance R.sub.1. Therefore, when a short circuit occurs between the signal lines 105 and 106 connected to the squib 102, it is difficult to detect the short circuit.